Wade Barrett seems like a very sound option. Problem is, the last three Rumbles featured winners who ended up competing for the WHC at WM. I have a funny feeling the winner of the upcoming Mania will be someone who goes for the WWE Championship.
If I had to guess. I wouldn't be surprised if John Cena wins the WWE title from Punk at Survivor Series or TLC. Then they can do Rock vs Cena II at the Royal Rumble. Rock wins again and becomes the new champion. CM Punk wins the Royal Rumble and faces The Rock at Wrestlemania.
Or not. They can always spoon-feed Cena another Rumble win, leading up to another WM main event where he can overcome the odds and beat Rock for the title. Wouldn't that be ever so wonderful?